Dry paint often comes in contact with itself especially in window and door areas and, depending on its hardness, the pressure, temperature, humidity, and duration of time which the surfaces are in contact, the painted surfaces sometimes stick together. This undesirable sticking together of two painted surfaces when pressed together or placed in contact with each other is referred to as "blocking". Thus, an important characteristic of coatings is block resistance.
A crosslinked coating composition with a high degree of entanglement (higher viscosity) would be expected to have greater block resistance than a coating composition with few entanglements (low viscosity). For these reasons, silane monomers have been used to provide crosslinking in polymer compositions. U.S. Pat. No. 3,729,438 describes an aqueous dispersion of a crosslinkable emulsion polymer prepared from vinyl acetate and a vinyl hydrolyzable silane. Upon removal of water from the emulsion polymer, the polymer crosslinks.
U.S. Pat. No. 3,706,697 describes an emulsion polymerization product of an acryloxyalkylsilane monomer with an alkyl acrylic ester wherein a silane is introduced to the polymerization after a portion of the other monomers are polymerized. International Patent Application WO 97/15624 describes curable aqueous compositions prepared with an emulsifiable polymer having pendant and/or terminal silyl ester groups and pendant terminal acidic groups neutralized with fugitive bases.
Japanese Patent Application No. 6025502 describes a composition containing a polymer emulsion obtained by adding a tin catalyst (a diorganotin carboxylate) which is insoluble in water, to silylated vinyl polymers after emulsion polymerization.
The disadvantages of using such alkoxy silane monomers, however, are that (1) the alkoxy silane monomers may crosslink during the emulsion polymerization and form grit; (2) the alkoxy silane monomers may hydrolyze during the emulsion polymerization so that even if the alkoxy silane monomer was polymerized the reactivity necessary for subsequent cross-linking would be destroyed; or (3) the alkoxy silane modified emulsion polymer may hydrolyze during storage.
Copending commonly assigned U.S. patent application Ser. No. 09/166,050, filed Oct. 5, 1998, describes a pressure sensitive adhesive which is prepared by emulsion polymerizing an ethylenically unsaturated monomer and 0.01 to 2 pphm of a sterically hindered alkoxylated silane monomer.
There continues to be a need for coating compositions which provide improved block resistance, and provide increased shelf life without the disadvantages present in prior art coating compositions.